This invention is particularly directed to improvements to hollow head log debarkers of the type as comprehended, for example, by U.S. Pat. No. 2,857,945, the disclosure of which is hereby incorporated by reference in its entirety. The principal of that prior art machine is that logs while being restrained from rotating are axially inserted into a hollow head. Blunt, individually tensioned bark tools mounted in the head are then rotated around the log as the log is fed through the hollow head. The compressive force between the tool and the bark produces a shearing force higher than the strength of the intermediate sap peel, the so-called cambium layer, thus, stripping the bark off of the log. The working parts of the machine consist of the rotor which carries the shafts of the barking tools and which rotates around the log during the debarking process, and a feed mechanism for feeding the logs through the rotor. The feed mechanism comprises six feed arms each with spiked rolls, three on the infeed side of the rotor and three on the outfeed side. The rotor is carried in a ball bearing and is driven by poly-V belts from the drive shaft.
The feed rolls were driven through a ring gear and pinion arrangement by a chain which runs inside the rotor housing and is also driven by a belt from the drive shaft. Thus, the feed rolls were tied together so that all of the rolls would turn at exactly the same speed. Where the logs were uneven in any respect the logs were either not fed through or the debarker suffered a mechanical breakdown. A linking system further insured that the feed rolls in each of the two sets were maintained an equal distance from the longitudinal axis of the rotor. A pair of rubber tension cylinders were used to keep the linking system tensioned.
The rotor bearing and the feed roll bearings ran in an oil bath. The oil, which was a high viscosity oil, (90 SAE) for the rotor bearing was carried up from the bath to the bearing by the feed rolls driving chain, this being lubricated at the same time. The barking tools were opened automatically by a projecting lip on the infeed side, the barking pressure being produced by rubber bands stretched between the tool shaft levers and pegs on the tension ring. By merely turning the ring, the pressure on all of the tools was uniformly increased or decreased.
Inasmuch as in the past all logs brought to debarking facilities were prime, short logs straight with few knots or protrusions and well groomed, the prior method of tying all six feeding spike rolls together with no latitude in individual movement proved sufficient. Additionally, the manufacturing facilities were of a lower production than is needed to meet today's plant requirements. The feed speed of the prior machines was slow and in all cases was one hundred and fifty feet per minute or less. The impact loading of the feed rolls was low because of these low feed speeds and of the short logs used which created a minimum of impact to the rigid mounted feed rolls and tools. The prevailing thought was that only prime logs in short log form with very few knots could produce good lumber. There were no tops also because they were sent to a large drum type debarker in short wood form. In these drums a number of short logs were threaded simultaneously and the bark was removed by the friction of the logs against each other and against the walls of the drum as the drum was rotated. Also no swell butts were sent to the prior machines because they were either left in the forest or sent to those debarking drums. This prior machine as described in the aforementioned patent performed well by the standards set for that era for which it was designed, built and used, but now a shortage of fiber requires a new era of debarking machines.
The lack of sufficient manpower to work in forest log selection has left only one viable method--total tree harvesting, that is, stripping the land of all of its fiber and bringing all this product to one location called the merchandising facility where all trees, regardless of length, size, sweep, knots, swelled butts, or kinorshum, have to be run through a hollow head debarker and either cut to log length and sent to a solid fiber (lumber or plywood) processing facility or chipped for the pulp industry. High labor costs have made it impractical to be selective in tree selection, and thus all logs are now brought to the log processing facility. Also, because of labor and capital costs, there are fewer plants and production at each plant has to increase which means that each debarker must increase in speed up to about 300 feet per minute. This increase in speed must also be made in view of the deteriorating quality of the logs to be debarked. This has caused shock loading to the feed means, the self opening tools, the rotor, and throughout the entire machine. The prior debarkers with their rollers operating at the same speeds could not handle these uneven logs. Expensive down time and maintenance costs have resulted and in some cases extra machines have to be supplied for the manufacturing operations. It was also found that the prior machines would not develop sufficient force required to feed an entire tree-length log through the debarking apparatus at high enough speeds. Also, inasmuch as the cost for manufacturing the debarking machines is great, it is preferable, where possible to retrofit existing machines to meet these new conditions in this new era of debarking machines.
In past machines, the bearings on which the rotor rotated were lubricated by an oil system which used a chain that dipped into an oil sump and carried the oil to the top of the bearing at which time the high viscosity contaminated oil then fell over the bearings and back to the oil sump. It was found that bark, dust, and other contaminants were not being flushed out of the system. The oil being used was of a very high viscosity and did not act as a flushing agent to flush out these contaminants and thus the life of the bearings was shortened. It was also difficult to maintain a proper flow of oil over the bearings.
It should also be noted that in the prior machines a rubber type cylinder or air cylinders with inefficient operating features were used with the tension linkage means to keep the arms and rollers in constant contact with the log. These rubber type or air cylinders did not provide the necessary shock dampening means. They also did not provide a quick open jog for quickly opening the arms when an obstruction was met.